Solution-based formation of a nanostructured, carbon-coated, inorganic composite

ABSTRACT

A process for solution-based formation of a nanostructured, carbon-coated, inorganic composite includes selecting a supply of inorganic material in a solution, selecting a supply of a carbon-containing solution, and synthesizing the composite by causing the inorganic material to react in the carbon-containing solution. The synthesized composite may be conductive-carbon-coated, and may be for electrochemical applications such as battery cathodes and anodes. The selecting step may involve varying relative amounts of polar fluid, microblender and water components to synthesize a crystalline inorganic composite. There may be a step of retaining and reusing the supply of carbon-containing solution that remains after the synthesizing, and testing the supply of carbon-containing solution that remains to determine whether it can be used again. There may be steps of controlling the composite particle size and morphology and forming desired particle size as a function of the chemical composition of the carbon-containing solution.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Patent Application Ser. No. 62/298,962, filed Feb. 23, 2016and U.S. Provisional Patent Application Ser. No. 62/393,591, filed Sep.12, 2016, each of which is hereby incorporated by reference in itsentirety for all purposes.

TECHNICAL FIELD

The disclosure relates to the field of materials science and, moreparticularly, to solution-based methods of forming nanocomposites.

BACKGROUND

Lithium Ion Battery (LIB) composites are made using several conventionalsynthesizing methodologies, including: (i) solid-state reaction; (ii)carbothermal reduction; (iii) solution-based methods that employhydrothermal/solvothermal, sol-gel, or co-precipitation; (iv)precipitation; and (v) emulsion drying. Each of the above methodologieshas undesirable aspects that can be characterized generally as requiringrelatively high cost raw materials, relatively high operating orreaction temperatures of >100° C., a relatively complex number of stepsthat includes a step of crushing, milling, grinding, mechanicallymixing, or blending to produce the inorganic composite.

SUMMARY

The invention can be characterized as a process for solution-basedformation of a nanostructured, carbon-coated, inorganic composite. Thatprocess includes selecting a supply of inorganic material in a solution,selecting a supply of a carbon-containing solution, and synthesizing thecomposite by causing the inorganic material to react in thecarbon-containing solution.

The invention may also be characterized as the product made by the aboveprocess. The synthesized composite may be conductive-carbon-coated, andmay be LFP or NMC for electrochemical applications such as cathodes. Theselecting step may involve varying relative amounts of polar fluid,microblender and water components to synthesize a crystalline inorganiccomposite. There may be a step of retaining and reusing the supply ofcarbon-containing solution that remains after the synthesizing, andtesting the supply of carbon-containing solution that remains todetermine whether it can be used again. There may be steps ofcontrolling the composite particle size and morphology and formingdesired particle size as a function of the chemical composition of thecarbon-containing solution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram illustrating the process of theinvention.

FIG. 2 is a schematic block diagram that illustrates another version ofthe process of the invention.

FIG. 3 is a schematic block diagram that illustrates another version ofthe process of the invention.

FIG. 4 is a schematic diagram showing use of recycled blendstock.

FIG. 5 shows the LiFePO₄/C composite characterized using XRD andelectrochemical performance.

FIG. 6 shows the LiFePO₄/C composite characterized using SEM andelectrochemical performance.

FIG. 7 is a schematic diagram showing the cycling study of LiFePO₄/Cmaterial assembled into a coin cell.

FIG. 8 is a schematic diagram showing cell voltage versus lithium as afunction of capacity for various C-rates.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, an embodiment of the invention is shown at 100 andis a process for solution-based formation of a nanostructured,carbon-coated, inorganic composite. Process 100 includes at 102,selecting a supply of inorganic material in a solution, at 104,selecting a supply of a carbon-containing solution including renewablefatty acids and naturally derived alcohols and, at 106 synthesizing ananostructured, carbon-coated, inorganic composite by, at 108, causingthe supply of inorganic material to react in the presence of thecarbon-containing solution.

Selecting step 102 may involve selecting a supply of thecarbon-containing solution that includes a fatty acid. The selectedcarbon-containing solution may also include a polar fluid component, amicroblender component and a water component, and each of thosecomponents are further described in co-pending U.S. patent applicationSer. No. 14/318,365 (“the Co-Pending Application”), and will bedescribed further below, after a discussion of FIGS. 1-3.

Still referring to FIG. 1, selecting step 104 may also involve varyingthe relative amounts of the polar fluid, microblender and watercomponents so that synthesizing step 106 produces a crystallineinorganic composite. Synthesizing step 106 may also involve synthesizinga crystalline inorganic composite. After the synthesizing step ispracticed, there remains an amount of the carbon-containing solution,which could be discarded using suitable methods. However, FIG. 2 showsan embodiment of the invention that provides an alternative todiscarding the remaining amount of the carbon-containing solution.

Referring to FIG. 2, another embodiment of the invention is shown at200, and is also a process like process 100, including selecting steps202 and 204, like selecting steps 102 and 104 of FIG. 1, and asynthesizing step 206, like synthesizing step 106 of FIG. 1. However,unlike process 100, process 200 also includes at 208, retaining thesupply of carbon-containing solution that remains after thesynthesizing. Retaining step 208 may also include at 210, testing thesupply of carbon-containing solution that remains to determine whetherit can be used again. Such testing could including any suitable,commercially available method, including, for example, GC, GCMS, and LC.Process 200 also includes at 212, repeating the synthesizing by causingthe inorganic materials to react in the presence of the retainedcarbon-containing solution.

Referring to FIG. 3, another embodiment of the invention is shown at300, and is also a process like process 100, including selecting steps302 and 304, like selecting steps 102 and 104 of FIG. 1. There is also asynthesizing step 306, like synthesizing step 106 of FIG. 1. However,synthesizing step 306 involves synthesizing a nanostructured,carbon-coated, crystalline inorganic composite.

Still referring to FIG. 3, synthesizing step 306 includes at 308,controlling the particle size and morphology of the composite. Thecontrolling may involve, as at 310, forming desired particle size as afunction of the chemical composition of the carbon-containing solution.Changes in the chemical composition of the carbon-containing solutionproduce changes in the particle size, morphology, and in some cases thecomposition of the synthesized composite.

Referring generally to FIGS. 1-3, the invention may also becharacterized as a nanostructured, carbon-coated, inorganic compositeformed by the above-described process. The process and the inorganiccomposite of the invention may have electrochemical applications, suchas to synthesize a nanostructured, conductive-carbon-coated, inorganiccomposite that is suitable for electrochemical applications.

One of those applications could be for use as a cathode in a batteryand, for that use, the process could be practiced to synthesize batterycomposites, such as battery-cathode or battery-anode composites.Battery-cathode composites may include Lithium Iron Phosphate(LFP)(LiFePO₄), Lithium Nickel Manganese Cobalt Oxide (NMC)(LiNiMnCoO₂),Lithium Cobalt Oxide (LCO)(LiCoO₂), Lithium Manganese Oxide(LMO)(LiMn₂O₄), and Lithium Nickel Cobalt Aluminum Oxide(NCAO)(LiNiCoAlO₂). Battery-anode composites could include LithiumTitanate (LTO)(Li₄Ti₅O₁₂).

For electrochemical applications, the selecting step 102, 202, 302 wouldinvolve selecting a supply of conductive-carbon-containing solution.

Referring generally to selecting steps 102, 202 and 302, the selectedcarbon-containing solution may, as noted above, also include a polarfluid component, a microblender component and a water component. Amixture of these three components is also referred to herein as ablendstock or microblend. As further described in the Co-PendingApplication, the polar fluid component may include one or more polarfluids, such as alcohols like ethanol. For example, the polar fluid mayinclude ethanol of a relatively low grade, and those low grades willalso have a water component. Ethanols of a low grade have a watercontent of 5-20%, assuming water is the main contaminant.

The polar fluid component may involve selecting an alcohol from a groupcomprising (a) n-propyl alcohol, (b) iso-propyl alcohol, (c) n-butylalcohol, a mixed alcohol formulation (e.g., ENVIROLENE®), methanol, andethanol, and blending the alcohol and the water component to form theone or more polar fluids. Blending the alcohol and water may involveformulating the amount of water so that the amount of water comprisesabout 1-30% of the one or more polar fluids. Preferably, the amount ofwater comprises about 5-20% of the one or more polar fluids. Preferably,the alcohol component includes ethanol. ENVIROLENE® is a mixed alcoholformulation made by Standard Alcohol Company of America. Examples ofsuitable mixed alcohol formulations are described in U.S. Pat. No.8,277,522 and published U.S. Patent Application No. 2013/0019519, whichare hereby incorporated by reference.

The microblender component may be a fatty acid, such as one chosen froma group comprising saturated and/or unsaturated carboxylic acids and/oresters containing 14 to 24 carbons, such as oleic acid, elaidic acid,erucic acid, linoleic acid, lauric acid, myristic acid, and stearicacid. The microblender may also be a fatty acid chosen from a groupcomprising suitable unsaturated or saturated fatty acids.

A neutralizer may also be combined with the polar fluid, microblenderand water components, and the neutralizer is chosen for its capabilityof neutralizing the microblender component. For example, the neutralizermay involve selecting a component of a lower pH than the microblendercomponent. For example, if the microblender component includes an acidiccomponent, then selecting the neutralizer may involve selecting a basiccomponent. Preferably, the neutralizer includes an ammonia component,such as ammonium hydroxide.

EXAMPLE

An application of the process of the invention was made by synthesizingLiFePO₄/C lithium ion battery cathode materials in recyclable,reverse-micelle media. The process allows for control of particle sizeand morphology, lower reaction temperature, improves electrochemicalperformance, provides a carbon coating for improved electricalconductivity, and provides for a recyclable reaction medium.

The use of recycled blendstock is shown in FIG. 4.

General Procedure of Solution-Based Nanostructured Material Formation

An iron salt (may be Fe(II) or Fe(III); in this example FeCl₂.4H₂O wasused) was dissolved in ethanol or ethanol/water mixtures at ˜0.5 mmol/mLThe salt concentration affects the crystalline structure of thesynthesized inorganic composite. To that solution, ˜2× by volume ofblendstock was added and the mixture was heated at 60° C. for 1 hour.Separate solutions were prepared containing: (i) 85% H₃PO₄ (ammoniumdihydrogen phosphate may also be used) at 1 mmol/mL in ethanol; and (ii)a lithium salt (e.g., lithium acetate, lithium acetylacetonate, lithiumiodide, lithium chloride, lithium hydroxide) at 1 mmol/mL in ethanol orethanol/water mixtures. The solutions were simultaneously added dropwiseto the mixture containing the iron salt and blendstock with constantstirring, then heated to 120° C. for 2 hours, and then transferred to aTeflon® flask and heated to 250° C. for 4 hours. The flask was allowedto cool to room temperature, the resulting cake was washed with water,and allowed to dry in an oven at 120° C. for 8 hours.

The resulting solid was ground into a powder and placed in an aluminacrucible and heated to 700° C. under Ar/H₂ for 4 hours to giveLiFePO₄/C. The LiFePO₄/C composite was characterized using XRD, SEM, andelectrochemical performance, and the results of those tests are shown inFIGS. 5 and 6.

Electrochemical Performance

The LiFePO₄/C composite was vacuum dried overnight at 100° C. and tapecast with binder and conductive additive and assembled into a coin cellwith a lithium counter electrode. The cell was full charged and thendischarged to 2.5 V versus Li at various C-rates. FIGS. 7-8 showrespectively, a schematic diagram of the cycling study of LiFePO₄/Cmaterial assembled into a coin cell, and a schematic diagram of cellvoltage versus lithium as a function of capacity for various C-rates.

The invention may also be described in the following number paragraphs.

1. A process for solution-based formation of a nanostructured,conductive-carbon-coated, inorganic, composite, cathode material,comprising:

selecting a supply of inorganic material in a solution;

selecting a supply of a conductive-carbon-containing solution; and

synthesizing a nanostructured, conductive-carbon-coated, inorganic,composite cathode material by causing the supply of inorganic materialto react in the presence of the conductive-carbon-containing solution.

2. The process of 1, wherein the selecting step involves selecting asupply of the carbon-containing solution that includes a fatty acid.

3. The process of 2, wherein the selecting step involves selecting asupply of a carbon-containing solution that includes a polar fluidcomponent, a microblender component and a water component.

4. The process of 2, wherein the synthesizing step involves synthesizinga crystalline inorganic composite.

5. The process of 4, wherein the selecting step also involves varyingthe relative amounts of the polar fluid, microblender and watercomponents so that the synthesizing step produces a crystallineinorganic composite.

6. The process of 5, further including the step of retaining the supplyof carbon-containing solution that remains after the synthesizing.

7. The process of 6, wherein the retaining step includes testing thesupply of carbon-containing solution that remains to determine whetherit can be used again.

8. The process of 7, further including the step of repeating thesynthesizing by causing the inorganic materials to react in the presenceof the retained carbon-containing solution.

9. The process of 1, wherein the synthesizing step includes controllingthe particle size and morphology of the composite.

10. The process of 9, wherein the controlling involves forming desiredparticle size as a function of the chemical composition of thecarbon-containing solution.

11. The process of 1, wherein the selecting step involves selecting asupply of conductive-carbon-containing solution.

12. The process of 11, wherein the synthesized composite is chosen fromthe group consisting of LFP, NMC, LCO, LMO, and NCA.

13. A nanostructured, conductive-carbon-coated, inorganic, compositecathode material formed from a solution-based reaction, comprising:

selecting a supply of inorganic material in a solution;

selecting a supply of a conductive-carbon-containing solution; and

synthesizing a nanostructured, conductive-carbon-coated, inorganic,composite cathode material by causing the supply of inorganic materialto react in the presence of the conductive-carbon-containing solution.

14. The composite cathode material of 13, wherein the selecting stepinvolves selecting a supply of the carbon-containing solution thatincludes a fatty acid.

15. The composite cathode material of 14, wherein the selecting stepinvolves selecting a supply of a carbon-containing solution thatincludes a polar fluid component, a microblender component and a watercomponent.

16. The composite cathode material of 14, wherein the synthesizing stepinvolves synthesizing a crystalline, inorganic, composite, cathodematerial.

17. The composite cathode material of 16, wherein the selecting stepalso involves varying the relative amounts of the polar fluid,microblender and water components so that the synthesizing step producesa crystalline, inorganic, composite, cathode material.

18. The composite cathode material of 17, further including the step ofretaining the supply of carbon-containing solution that remains afterthe synthesizing.

19. The composite cathode material of 18, wherein the retaining stepincludes testing the supply of carbon-containing solution that remainsto determine whether it can be used again.

20. The composite cathode material of 19, further including the step ofrepeating the synthesizing by causing the inorganic materials to reactin the presence of the retained carbon-containing solution.

21. The composite cathode material of 13, wherein the synthesizing stepincludes controlling the particle size and morphology of the compositecathode material.

22. The composite cathode material of 21, wherein the controllinginvolves forming desired particle size as a function of the chemicalcomposition of the carbon-containing solution.

23. The composite cathode material of 13, wherein the selecting stepinvolves selecting a supply of conductive-carbon-containing solution.

24. The composite cathode material of 23, wherein the synthesizedcomposite cathode material is chosen from the group consisting of LFPand NMC.

In the preceding description, various aspects of claimed subject matterhave been described. For purposes of explanation, specific numbers,systems and/or configurations were set forth to provide a thoroughunderstanding of the claimed subject matter. However, it should beapparent to one skilled in the art having the benefit of this disclosurethat claimed subject matter may be practiced without the specificdetails. In other instances, features that would be understood by one ofordinary skill were omitted and/or simplified so as not to obscureclaimed subject matter. While certain features have been illustratedand/or described herein, many modifications, substitutions, changesand/or equivalents will now occur to those skilled in the art. It is,therefore, to be understood that the appended claims are intended tocover all such modifications and/or changes as fall within the truespirit of claimed subject matter.

We claim:
 1. A process for solution-based formation of a nanostructured,carbon-coated, inorganic composite, comprising: selecting a supply ofinorganic material in a solution; selecting a supply of acarbon-containing solution; and synthesizing a nanostructured,carbon-coated, inorganic composite by causing the supply of inorganicmaterial to react in the presence of the carbon-containing solution. 2.The process of claim 1, wherein the selecting step involves selecting asupply of the carbon-containing solution that includes a fatty acid. 3.The process of claim 2, wherein the selecting step involves selecting asupply of a carbon-containing solution that includes a polar fluidcomponent, a microblender component and a water component.
 4. Theprocess of claim 2, wherein the synthesizing step involves synthesizinga crystalline inorganic composite.
 5. The process of claim 4, whereinthe selecting step also involves varying the relative amounts of thepolar fluid, microblender and water components so that the synthesizingstep produces a crystalline inorganic composite.
 6. The process of claim5, further including the step of retaining the supply ofcarbon-containing solution that remains after the synthesizing.
 7. Theprocess of claim 6, wherein the retaining step includes testing thesupply of carbon-containing solution that remains to determine whetherit can be used again.
 8. The process of claim 7, further including thestep of repeating the synthesizing by causing the inorganic materials toreact in the presence of the retained carbon-containing solution.
 9. Theprocess of claim 1, wherein the synthesizing step includes controllingthe particle size and morphology of the composite.
 10. The process ofclaim 9, wherein the controlling involves forming desired particle sizeas a function of the chemical composition of the carbon-containingsolution.
 11. The process of claim 1, wherein the selecting stepinvolves selecting a supply of conductive-carbon-containing solution.12. The process of claim 11, wherein the synthesizing produces ananostructured, conductive-carbon-coated, inorganic composite that issuitable for electrochemical applications.
 13. The process of claim 12,wherein the synthesized composite is suitable for use as a batterycomposite.
 14. The process of claim 13, wherein the synthesizedcomposite is chosen from the group of battery composites consisting ofbattery-cathode and battery-anode composites.
 15. The process of claim13, wherein the synthesized group of battery-cathode compositesconsisting of LFP, NMC, LMO, LCO and NCAO.
 16. The process of claim 13,wherein the battery-anode composite is LTO.
 17. A nanostructured,carbon-coated, inorganic composite formed from a solution-basedreaction, comprising: selecting a supply of inorganic materials in anaqueous solution; selecting a supply of a carbon-containing solution;and synthesizing a nanostructured, carbon-coated, inorganic composite bycausing the supply of inorganic materials to react in the presence ofthe carbon-containing solution.
 18. The composite of claim 17, whereinthe selecting step involves selecting a supply of the carbon-containingsolution that includes a fatty acid.
 19. The composite of claim 18,wherein the selecting step involves selecting a supply of acarbon-containing solution that includes a polar fluid component, amicroblender component and a water component.
 20. The composite of claim18, wherein the synthesizing step involves synthesizing a crystallineinorganic composite.
 21. The composite of claim 20, wherein theselecting step also involves varying the relative amounts of the polarfluid, microblender and water components so that the synthesizing stepproduces a crystalline inorganic composite.
 22. The composite of claim21, further including the step of retaining the supply ofcarbon-containing solution that remains after the synthesizing.
 23. Thecomposite of claim 22, wherein the retaining step includes testing thesupply of carbon-containing solution that remains to determine whetherit can be used again.
 24. The composite of claim 23, further includingthe step of repeating the synthesizing by causing the inorganicmaterials to react in the presence of the retained carbon-containingsolution.
 25. The composite of claim 17, wherein the synthesizing stepincludes controlling the particle size and morphology of the composite.26. The composite of claim 25, wherein the controlling involves formingdesired particle size as a function of the chemical composition of thecarbon-containing solution.
 27. The composite of claim 26, wherein theselecting step involves selecting a supply ofconductive-carbon-containing solution.
 28. The composite of claim 27,wherein the synthesizing produces a nanostructured,conductive-carbon-coated, inorganic composite that is suitable forelectrochemical applications.
 29. The composite of claim 28, wherein thesynthesized composite is suitable for use in the group consisting of abattery cathode and battery anode.
 30. The composite of claim 29,wherein the synthesized composite is chosen from the group consisting ofLFP, NMC, LMO, LCO, NCAO, and LTO.